Heat transfer and precipitation means



Oct. 18, 1949. H. c. COOPER HEAT TRANSFER AND PRECIPITATION MEANS 2 Sheets-Sheet 1 Filed D60. 22. 1945 INVENTQR Howsu. C. COOPER BY ga /L 1 mm Tosca ATTORNEY Em m N E & -m M w mm Em 0 MR 11'] s W m M m w b ||l|-|.||-|I G H JL L 5 IIIIB 2 A 0 a 3 3 Mm E ET. M mm m m 5 IH Q 0 0 IER J. L G R a LM 4 U P v w m E T m T w N m E P N v a m u 1 HEAT TRANSFER AND PRECIPITATION MEANS Oct. 18, 1949.

Filed Dec. 22, 1945 NATURAL GAS NATURAL GAS' INVENTOR HOWELL C. COOPER BY:

Patented Oct. 18, 1949 UNITED STATES PATENT OFFICE Howell C. Cooper, Sewickley, Pa.

Application December 22, 1945, Serial No. 637,045

1 Claim.

This invention relates to heat transfer and precipitation means and more particularly to gas-togas transfer of sensible heat, accomplished by contact of the gas to be processed, with a condensant liquid of low vapor pressure moving at approximately uniform pressure in a condensant cycle, the cycle providing cooling of the condensant before said contact and separation of the resultant condensate from said condensant after contact.

The invention is applicable, as will appear, to the refrigeration art and especially the cascade type of multistage refrigeration. Further, it is applicable to very large quantities of gas and in transferring large amounts of heat; so that it is especially adapted in the liquefaction of natural gases for storage purposes, both as a precoolant for the natural gas, for removal of condensable constituents therefrom before liquefaction, and for interstage heat transfer in the refrigeration system employed in liquefying the natural gas.

The general objects of the invention therefore are to provide a preliquefaction treatment of a gas such as natural gas, involving both precooling of the gas and removal of constituents such as water and carbon dioxide therefrom, in the most effective and economical manner possible; and to such end to provide a heat transfer and precipitation cycle applicable not only to the natural gas to be liquefied, but useful also in the refrigerationsystem involved in the liquefaction. As will appear, effectively the only net heat lssif it can be considered a lossis the refrigeration necessary to solidify the carbon dioxide and liquefy the water to be removed.

Another object of the invention is the selection of a suitable condensant for the purpose intended.

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawings in which Fig. 1 is a conventionalized flow diagram of refrigerant treating portions of a natural gas liquefaction system of a capacity in the order of sixty million cubic feet per day,

Fig. 2 is a similar diagrammatic showing of other portions, particularly carbon dioxide and water removing portions, of the same system; the line A--B, Figs. 1 and 2, indicating the location of interconnection of the two separately illustrated portions, to form the complete system.

Fig. 3 is a similar showing of a modification of the portion of the system illustrated in Fig. 2; it being understood that the flow diagrams here apthe invention being equally applicable in other systems, as will be apparent to one familiar with the art. I

In the following description, recited temperatures are in degrees Farenhelt and pressures in pounds per square inch absolute, but it must be appreciated that such figures are recited by way of example only and maybe only approximately accurate, it being understood that in the practice of the art some latitude is usually available to the designer, as in the selection of both type and size of equipment units, and in their arrangement.

With reference now to the drawings and first to Fig. 2 thereof, the natural gas to be liquefied, consisting largely of methane, enters the system at l and moves successively upwardly through the contact coolers 2 and 3 and downwardly through the condenser 4, from the bottom of which it emerges as a liquid through the pipe 5; the entering pressure being 200 and temperature 70, and the emerging methane product being at a pressure of 20 and a temperature of-240.

For the purpose of substantially cooling the gas ahead of the condenser 4 and at the same time removing condensable constituents therefrom, such as water and carbon dioxide, a condensant is employed in a closed cycle of slight change in pressure, associated with the above described part of the system.

Requisites of the condensant are that it must stay liquid at temperatures low enough to condense the constituents to be eliminated and have suificiently low vapor pressure that substantially all of it will be retained in its own circuit, the circuit involving intimate contact with the gas being processed. -Also, it must be capable of entraining the condensates and yet permit easy separation of the latter therefrom. I have found that pentane, which does not solidify below 200 and the vapor pressure of which does not exceed 14.7 at 90, nicely serves as condensant for so processing natural gas, but doubtless others, 01 mingled liquids such as pentane, hexane, heptane and so on might be satisfactory for the purpose.

The condensant circuit includes a heat exchanger l0 wherein it is cooled and from which it flows at a pressure of 205, temperature of 170, sequentially through the contact cooler 3, the centrifuge ll, pump l2, contact cooler 2, centrifuge l3,'pump l4, and back to the top of heat exchanger Ill at a pressure of 218, temperature of 60.

,In the contact cooler 2, the natural gas moves upwardly and the condensant liquid downwardly, the two being in intimate contact with each other pearing are only for illustration of the invention, as by spraying or otherwise breaking up the condensant into particles falling through the gas as indicated in the drawing, or by spreading of the condensate over baflle plates exposed to the gas, or both, as will be well understood by one familiar with the art. At any. rate, the result is thatthe gas is so lowered in temperature as to condense water therefrom. This water passes downwardly from the contact cooler 2 with the condensant liquid, and is separated from the latter in the centrifuge I3 from which it is removed by way of the pipe [5. ,1 The condensant flows from the centrifuge |3 to the pump l4 by which it is delivered back 'to the heat exchanger Ill. The cooled dehydrated gas passes from the top of the cooler 2 and enters the bottom of the contact cooler 3.

In the contact cooler 3 the gas is further cooled, sufliciently to condense carbon dioxide therefrom, employing the condensant from the heat exchanger Ill. The condensant liquid enters near the top and leaves at the bottom with entrained carbon dioxide 'in the form of solid particles, separation takes place in the centrifuge II and the condensant is delivered by the pump l2 to the contact cooler 2, the separated carbon dioxide leaving the centrifuge entrained in water, as by the pipe l6. Generally the condensant may remove only sensible heat from the gas within the cooler 3, and a coilmay be arranged within the cooler to remove latent heat the coil being served by a refrigerant as will appear. The gas leaving the contact cooler 3 may be serviced before entering the condenser 4 by a centrifuge l8, and pump I9 in the auxiliary circuit indicated,

by which any condensate entrained therein is re moved.

For service of the main product condenser 4, as well as the coil H, a refrigerant such as methane is provided in a cycle involving gas and liquid phases, in a circuit including the condenser 20, Fig. 1, wherein the methane refrigerant is liquefied, and the line a, Figs. 1 and 2, leading from the condenser 26 to the condenser 4; this refrigerant returning to its gas phase within the condenser 4, to liquefy the product natural gas, and also in the coil H to condense out the carbon dioxide.

This methane refrigerant circuit leads from the condenser 4 through the heat exchanger ID to the return line b Figs. 1 and 2, and the methane leaves the heat exchanger Ill at a pressure of I! and temperature of 100. By means of the indicated, to the flash tank 3| where it has a 1 pressure of 62 at 200 temperature. a

A refrigerant gas bypass 32 leads upwardly from the flash tank 3| through the condenser 20 and into the second stage compressor 2| at a pressure of 62 and temperature of -140 J as indicated.

From the flash tank 3| the liquid methane refrigerant is drawn through the line a at a pressure of 62 and temperature of -200, past expansion valves 33 and 34 at a pressure of 20 and temperature of -252, which control respectively, refrigerant service of the natural gas within product condenser 4 and condensing coil I1 within the contact cooler 3.

The heat exchangers and 21, are served by a second refrigerant such as ethylene, in a cycle involving its gas-and liquid phases in acircuit generally similar to the methane circuit just described. Principal parts of this circuit are the compressors and 4|! and associated waterstaged compressors 2|, Zl and 2| and associated interstage contact coolers 22 22 and 22 the pressure is raised to 690 at which the methane enters the contact cooler 23. The contact coolers 22 22 and 22"are served by cooling water at a temperature of 62, entering by way of the line 24 and leaving by way of the line 25 at a temperature of 85. Water entrained in these interstage coolers is removed by a separator 26. At the same pressure the compressed gas is precooled to a temperature of 126 and water vapor removed therefrom in the contact cooler 23 by service of a liquid condensant such as propane, in a condensant circuit including a cooling heat exchanger 21 which it leaves at a pressure of 605 and a temperature of 130, ahead of the contact cooler 23, and a centrifuge 28 and pump 29 after the contact cooler 23, by which pump 29 the condensant is returned to the heat exchanger 21 at a pressure of 618 and temperature of 90. Action within the contact cooler 23 is generally as described in connection with the contact cooler 2. Water is condensed out of the upwardly flowsrved contact coolers 4|, 4|, the contact cooler. 42, wherein preliquefactic-n cooling takes place and water picked up'in the coolers 4| and 42 is condensed out, the liquefying condenser 43, and

flash tank 44 with associated expansion valve 44.

The ethylene refrigerant, in liquid phase at a pressure of 82, and a temperature, leaves the valve 3|] and enters the heat exchanger 30 at a pressure of 20, temperature of 145, and leaves the heat exchanger 2'! at a pressure of 1'7, temperature of 80, enters the contact cooler 42 at 355 pressure, temperature, leaves the contact cooler at a '8 without substantial pressure change, and leaves the condenser 43 in liquid phase.

The contact cooler 42 is served by a condensant liquid such as pentane cooled in the heat ex-- changer 45 to a temperature of ---12 at a pressure of 360 in a circuit including the centrifuge 46 and pump 41 by which the ethylene refrigerant is precooled ahead of the condenser 43 and its water removed, the condensant reentering the heat exchanger 45 at a perature of 90.

Since the general manner of operation of the ethylene in its circuit is similar to that of the methane in its described circuit, it is thought that further description of the ethylene circuit is unnecessary, to one familiar with the art.

appears in Fig. 3 is in substitution of What appears in Fig. 2, effectively to the left of line A-B, Fig. 1, similar parts in the figures bearing similar reference characters.

in the arrangement of Fig. 3 separate condenpressure of 3'73 and a temsant liquids are employed, in separate circuits, for

removing the water and carbon dioxide respec- The propane serves the contact cooler 3 for further cooling of the product gas, and condensation and removal of the carbon dioxide also generally as before, being itself cooled, however, by its own heat exchanger Ill. The heat exchangers 3, and Ill and iii are arranged in series relation in the methane refrigerant circuit ahead of its first compressor 2E.

The advantage of this modified arrangement is that, since propane can be cooled much lower than can pentane, employment of propane for condensation of the carbon dioxide in the contact cooler 3, permits removal of the latent heat of the carbon dioxide without necessitating the coil I l of Fig. 1 for that purpose.

I claim: v

In a natural gas liquefaction system including a product condenser served by a recirculating refrigerant: means efiectlve on said gas ahead of said condenser for precipitation of condensable ingredients from the methane in the gas and including means for circulating a condensant liquid of low vapor pressure in a circuit providing successive cooling of said condensant by said refrigerant after said refrigerant leaves said product condenser, contact between said gas and said condensant, and removal of the resultant condensate from said condensant. I

HOWELL C. COOPER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,739,750 Carney Dec. 17, 1929 1,808,494 Carney et al June 2, 1931 2,022,165 Twomey Nov. 26, 1935 2,090,163 Twomey Aug. 1'7, 1937 2,141,997 Linde et a1 Dec. 2'7, 1938 2,198,142 Wade Apr. 23, 1940 2,252,738 Stoever Aug. 19, 1941 

